Well, you have me on a new hobby of collecting third-party apps for the Fire now (next, if Amazon doesn't get rid of the grey bar on non-amazon videos,

ApK

What grey bar??
I simply convert my personal videos to Mpeg4 and sideload them via USB they play fine no grey bar on my Kindle.

Edited to Add: I think I see what you mean the thin little bar at the bottom to bring up the home screen button
is not an Issue for me personally as I do my movie watching at home and any
on the go watching on a 7 inch device can be done with the thin little bar in place considering the nature of mobile video devices.